Developing Normative Data for Tone Burst ABR

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Answer

While the manufacturer will typically provide default dB nHL values, these values are only valid for the exact parameter settings used to obtain them. You are wise to want to check the dB nHL values within your own test setting and using your test parameters, in order to have the most accurate estimation of thresholds.

The type of normative data needed really depends on the purpose of the ABR testing. For neurodiagnostic ABR testing, normative data for latency values of individual waveform components must be obtained. Neurodiagnostic ABRs are typically recorded using a click stimulus. Based on your question, I am going to assume that you will be using tone-burst stimuli for threshold estimation. Therefore, the information you want to obtain is simply the verification of the equipment's dB nHL values. We know that 0 dB nHL represents normal hearing threshold for that stimulus. To verify that your equipment appropriately represents threshold, you should recruit a minimum of 10 normally hearing adults for a listening check. Using the same transducers and collection parameters that you implement during your ABR testing, present the tone-burst stimuli through the ABR equipment, and obtain behavioral thresholds for each stimulus frequency that you wish to use in the clinic. Once you have your thresholds for each individual at each tone-burst frequency, calculate a group average for each frequency. If the average threshold for the group is 0 dB, then you can be confident in the manufacturer's default values. However, if the average threshold is above or below this level, you will need to apply a correction factor to adjust for the difference.

I also recommend that you obtain separate thresholds for both right and left ears, as sometimes there are subtle differences between transducers which can affect the intensity of the stimulus presented. You may need to apply different correction factors for each transducer.

Dr. Tina Prout is an Assistant Professor at the University of Northern Colorado. She specializes in auditory electrophysiology. Her research is focused on the use of auditory evoked potentials to objectively assess auditory processing disorders.